Subject: [RFC PATCH 4/4] KVM: arm64: Introduce KVM_CAP_ARM_PROTECTED_VM

From: Will Deacon <[email-masked]>
Date: Thu, 3 Jun 2021 19:33:47 +0100

Introduce a new VM capability, KVM_CAP_ARM_PROTECTED_VM, which can be
used to isolate guest memory from the host. For now, the EL2 portion is
missing, so this documents and exposes the user ABI for the host.

Signed-off-by: Will Deacon <[email-masked]>
---
 Documentation/virt/kvm/api.rst    |  69 ++++++++++++++++++++
 arch/arm64/include/asm/kvm_host.h |  10 +++
 arch/arm64/include/uapi/asm/kvm.h |   9 +++
 arch/arm64/kvm/arm.c              |  18 +++---
 arch/arm64/kvm/mmu.c              |   3 +
 arch/arm64/kvm/pkvm.c             | 104 ++++++++++++++++++++++++++++++
 include/uapi/linux/kvm.h          |   1 +
 7 files changed, 205 insertions(+), 9 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 7fcb2fd38f42..dfbaf905c435 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6362,6 +6362,75 @@ default.
 
 See Documentation/x86/sgx/2.Kernel-internals.rst for more details.
 
+7.26 KVM_CAP_ARM_PROTECTED_VM
+-----------------------------
+
+:Architectures: arm64
+:Target: VM
+:Parameters: flags is a single KVM_CAP_ARM_PROTECTED_VM_FLAGS_* value
+
+The presence of this capability indicates that KVM supports running in a
+configuration where the host Linux kernel does not have access to guest memory.
+On such a system, a small hypervisor layer at EL2 can configure the stage-2
+page tables for both the CPU and any DMA-capable devices to protect guest
+memory pages so that they are inaccessible to the host unless access is granted
+explicitly by the guest.
+
+The 'flags' parameter is defined as follows:
+
+7.26.1 KVM_CAP_ARM_PROTECTED_VM_FLAGS_ENABLE
+--------------------------------------------
+
+:Capability: 'flag' parameter to KVM_CAP_ARM_PROTECTED_VM
+:Architectures: arm64
+:Target: VM
+:Parameters: args[0] contains memory slot ID to hold guest firmware
+:Returns: 0 on success; negative error code on failure
+
+Enabling this capability causes all memory slots of the specified VM to be
+unmapped from the host system and put into a state where they are no longer
+configurable. The memory slot corresponding to the ID passed in args[0] is
+populated with the guest firmware image provided by the host firmware.
+
+The first vCPU to enter the guest is defined to be the primary vCPU. All other
+vCPUs belonging to the VM are secondary vCPUs.
+
+All vCPUs belonging to a VM with this capability enabled are initialised to a
+pre-determined reset state irrespective of any prior configuration according to
+the KVM_ARM_VCPU_INIT ioctl, with the following exceptions for the primary
+vCPU:
+
+	===========	===========
+	Register(s)	Reset value
+	===========	===========
+	X0-X14:		Preserved (see KVM_SET_ONE_REG)
+	X15:		Boot protocol version (0)
+	X16-X30:	Reserved (0)
+	PC:		IPA base of firmware memory slot
+	SP:		IPA end of firmware memory slot
+	===========	===========
+
+Secondary vCPUs belonging to a VM with this capability enabled will return
+-EPERM in response to a KVM_RUN ioctl() if the vCPU was not initialised with
+the KVM_ARM_VCPU_POWER_OFF feature.
+
+There is no support for AArch32 at any exception level.
+
+It is an error to enable this capability on a VM after issuing a KVM_RUN
+ioctl() on one of its vCPUs.
+
+7.26.2 KVM_CAP_ARM_PROTECTED_VM_FLAGS_INFO
+------------------------------------------
+
+:Capability: 'flag' parameter to KVM_CAP_ARM_PROTECTED_VM
+:Architectures: arm64
+:Target: VM
+:Parameters: args[0] contains pointer to 'struct kvm_protected_vm_info'
+:Returns: 0 on success; negative error code on failure
+
+Populates the 'struct kvm_protected_vm_info' pointed to by args[0] with
+information about the protected environment for the VM.
+
 8. Other capabilities.
 ======================
 
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 7cd7d5c8c4bc..5645af2a1431 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -100,6 +100,11 @@ struct kvm_s2_mmu {
 struct kvm_arch_memory_slot {
 };
 
+struct kvm_protected_vm {
+	bool enabled;
+	struct kvm_memory_slot *firmware_slot;
+};
+
 struct kvm_arch {
 	struct kvm_s2_mmu mmu;
 
@@ -132,6 +137,8 @@ struct kvm_arch {
 
 	u8 pfr0_csv2;
 	u8 pfr0_csv3;
+
+	struct kvm_protected_vm pkvm;
 };
 
 struct kvm_vcpu_fault_info {
@@ -763,6 +770,9 @@ void kvm_arch_free_vm(struct kvm *kvm);
 
 int kvm_arm_setup_stage2(struct kvm *kvm, unsigned long type);
 
+int kvm_arm_vm_ioctl_pkvm(struct kvm *kvm, struct kvm_enable_cap *cap);
+#define kvm_vm_is_protected(kvm) (kvm->arch.pkvm.enabled)
+
 int kvm_arm_vcpu_finalize(struct kvm_vcpu *vcpu, int feature);
 bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
 
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 24223adae150..cdb3298ba8ae 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -402,6 +402,15 @@ struct kvm_vcpu_events {
 #define KVM_PSCI_RET_INVAL		PSCI_RET_INVALID_PARAMS
 #define KVM_PSCI_RET_DENIED		PSCI_RET_DENIED
 
+/* Protected KVM */
+#define KVM_CAP_ARM_PROTECTED_VM_FLAGS_ENABLE	0
+#define KVM_CAP_ARM_PROTECTED_VM_FLAGS_INFO	1
+
+struct kvm_protected_vm_info {
+	__u64 firmware_size;
+	__u64 __reserved[7];
+};
+
 #endif
 
 #endif /* __ARM_KVM_H__ */
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 8d5e23198dfd..186a0adf6391 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -83,22 +83,19 @@ int kvm_arch_check_processor_compat(void *opaque)
 int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 			    struct kvm_enable_cap *cap)
 {
-	int r;
-
-	if (cap->flags)
-		return -EINVAL;
-
 	switch (cap->cap) {
 	case KVM_CAP_ARM_NISV_TO_USER:
-		r = 0;
+		if (cap->flags)
+			return -EINVAL;
 		kvm->arch.return_nisv_io_abort_to_user = true;
 		break;
+	case KVM_CAP_ARM_PROTECTED_VM:
+		return kvm_arm_vm_ioctl_pkvm(kvm, cap);
 	default:
-		r = -EINVAL;
-		break;
+		return -EINVAL;
 	}
 
-	return r;
+	return 0;
 }
 
 static int kvm_arm_default_max_vcpus(void)
@@ -265,6 +262,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ARM_PTRAUTH_GENERIC:
 		r = system_has_full_ptr_auth();
 		break;
+	case KVM_CAP_ARM_PROTECTED_VM:
+		r = is_protected_kvm_enabled();
+		break;
 	default:
 		r = 0;
 	}
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index c5d1f3c87dbd..e1d4a87d18e4 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1349,6 +1349,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	bool writable = !(mem->flags & KVM_MEM_READONLY);
 	int ret = 0;
 
+	if (kvm_vm_is_protected(kvm))
+		return -EPERM;
+
 	if (change != KVM_MR_CREATE && change != KVM_MR_MOVE &&
 			change != KVM_MR_FLAGS_ONLY)
 		return 0;
diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index 7af5d03a3941..cf624350fb27 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -50,3 +50,107 @@ static int __init pkvm_firmware_rmem_init(struct reserved_mem *rmem)
 }
 RESERVEDMEM_OF_DECLARE(pkvm_firmware, "linux,pkvm-guest-firmware-memory",
 		       pkvm_firmware_rmem_init);
+
+static int pkvm_init_el2_context(struct kvm *kvm)
+{
+	kvm_pr_unimpl("Stage-2 protection is not yet implemented\n");
+	return -EINVAL;
+}
+
+static int pkvm_init_firmware_slot(struct kvm *kvm, u64 slotid)
+{
+	struct kvm_memslots *slots;
+	struct kvm_memory_slot *slot;
+
+	if (slotid >= KVM_MEM_SLOTS_NUM || !pkvm_firmware_mem)
+		return -EINVAL;
+
+	slots = kvm_memslots(kvm);
+	if (!slots)
+		return -ENOENT;
+
+	slot = id_to_memslot(slots, slotid);
+	if (!slot)
+		return -ENOENT;
+
+	if (slot->flags)
+		return -EINVAL;
+
+	if ((slot->npages << PAGE_SHIFT) < pkvm_firmware_mem->size)
+		return -ENOMEM;
+
+	kvm->arch.pkvm.firmware_slot = slot;
+	return 0;
+}
+
+static void pkvm_teardown_firmware_slot(struct kvm *kvm)
+{
+	kvm->arch.pkvm.firmware_slot = NULL;
+}
+
+static int pkvm_enable(struct kvm *kvm, u64 slotid)
+{
+	int ret;
+
+	ret = pkvm_init_firmware_slot(kvm, slotid);
+	if (ret)
+		return ret;
+
+	ret = pkvm_init_el2_context(kvm);
+	if (ret)
+		pkvm_teardown_firmware_slot(kvm);
+
+	return ret;
+}
+
+static int pkvm_vm_ioctl_enable(struct kvm *kvm, u64 slotid)
+{
+	int ret = 0;
+
+	mutex_lock(&kvm->lock);
+	if (kvm_vm_is_protected(kvm)) {
+		ret = -EPERM;
+		goto out_kvm_unlock;
+	}
+
+	mutex_lock(&kvm->slots_lock);
+	ret = pkvm_enable(kvm, slotid);
+	if (ret)
+		goto out_slots_unlock;
+
+	kvm->arch.pkvm.enabled = true;
+out_slots_unlock:
+	mutex_unlock(&kvm->slots_lock);
+out_kvm_unlock:
+	mutex_unlock(&kvm->lock);
+	return ret;
+}
+
+static int pkvm_vm_ioctl_info(struct kvm *kvm,
+			      struct kvm_protected_vm_info __user *info)
+{
+	struct kvm_protected_vm_info kinfo = {
+		.firmware_size = pkvm_firmware_mem ?
+				 pkvm_firmware_mem->size :
+				 0,
+	};
+
+	return copy_to_user(info, &kinfo, sizeof(kinfo)) ? -EFAULT : 0;
+}
+
+int kvm_arm_vm_ioctl_pkvm(struct kvm *kvm, struct kvm_enable_cap *cap)
+{
+	if (cap->args[1] || cap->args[2] || cap->args[3])
+		return -EINVAL;
+
+	switch (cap->flags) {
+	case KVM_CAP_ARM_PROTECTED_VM_FLAGS_ENABLE:
+		return pkvm_vm_ioctl_enable(kvm, cap->args[0]);
+	case KVM_CAP_ARM_PROTECTED_VM_FLAGS_INFO:
+		return pkvm_vm_ioctl_info(kvm, (void __user *)cap->args[0]);
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 3fd9a7e9d90c..58ab8508be5e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1082,6 +1082,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_SGX_ATTRIBUTE 196
 #define KVM_CAP_VM_COPY_ENC_CONTEXT_FROM 197
 #define KVM_CAP_PTP_KVM 198
+#define KVM_CAP_ARM_PROTECTED_VM 199
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.32.0.rc0.204.g9fa02ecfa5-goog

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